What is the electrolyte in the battery?

The battery is a device for energy conversion and storage. It converts chemical or physical energy into electrical energy through the reaction. A battery is a chemical power source. It consists of two electrochemical active electrodes of two different components. The two electrodes are immersed in electrolytes that provide media conduction. When connected to an external carrier, Provide energy by converting its internal chemical energy. As an electric storage device, when two metals(usual metals of different properties) are immersed in the electrolyte, they can conduct electricity and generate a certain electromotive force between the "polar plates". The electromotive force(or voltage) is related to the metal used, and the electromotive force of different types of batteries is also different.

The performance parameters of the battery mainly include electromotive force, capacity, specific energy, and resistance. The electromotive force is equal to the work done by the battery's non-static power(chemical force) when the unit positive charge is moved from the negative electrode to the positive electrode through the battery. The electromotive force depends on the chemical properties of the electrode material and has nothing to do with the size of the battery. The total amount of electricity that the battery can output is the capacity of the battery, usually in amperes hours. In the battery reaction, the electrical energy produced by 1 kilogram of reaction material is called the theoretical energy of the battery. The actual battery is smaller than the energy than the theory. Because the reactants in the battery are not all based on the battery reaction, and the resistance in the battery also causes the electromotive force to drop, it is often referred to as a high-energy battery. The larger the area of the battery, the smaller the internal resistance.

The battery's energy storage is limited. The total amount of electricity that the battery can output is called it's capacity. It is usually expressed in amperes hours. It is also a performance parameter of the battery. The capacity of the battery is related to the amount of electrode material, that is, the size of the electrode.

Practical chemical batteries can be divided into two basic types: primary batteries and batteries. After the primary battery is made, an electric current can be generated, but it is discarded after the discharge is completed. The battery, also known as the secondary battery, must be charged before use. After charging, it can be used for discharge. After discharge, it can also be charged and used again. When the battery is charged, electrical energy is converted into chemical energy; When discharged, chemical energy is converted into electrical energy.

The principle of the battery

In a chemical battery, the direct conversion of chemical energy to electrical energy is the result of spontaneous oxidation, reduction, and other chemical reactions within the battery. This reaction is carried out on two electrodes. Negative active substances consist of reducing agents that have negative potentials and are stable in electrolytes, such as active metals such as zinc, cadmium, and lead, as well as hydrogen or hydrocarbons. Positive active substances consist of oxidants with positive potentials and are stable in electrolytes, such as metal oxides such as manganese dioxide, lead dioxide, nickel oxide, oxygen or air, halogen, and its salts, oxic acid and its salts. Electrolytes are materials with good Ionic conductivity, such as aqueous solutions of acids, bases, and salts, organic or inorganic non-aqueous solutions, molten salts, or solid electrolytes. When the external circuit is disconnected, although there is a potential difference(open circuit voltage) between the two poles, there is no current, and the chemical energy stored in the battery is not converted into electrical energy. When the external circuit is closed, there is a current flowing through the external circuit under the action of the two electrode potential difference. At the same time, within the battery, because there are no free electrons in the electrolyte, the transfer of charge must be accompanied by the oxidation or reduction reaction of the interface between the polar active material and the electrolyte, and the material transfer of the reactants and reaction products. The transfer of charge in the electrolyte is also accomplished by the migration of ions. Therefore, the normal charge transfer and material transfer process inside the battery is a necessary condition to ensure the normal output of electrical energy. When charging, the direction of the internal transmission and mass transfer process of the battery is exactly the opposite of the discharge; The electrode reaction must be reversible in order to ensure the normal transfer of mass and electricity in the opposite direction. Therefore, the reversible electrode reaction is a necessary condition for the formation of a battery. Free energy increment(Coke) for Gibbs reaction; F is Faraday constant = 96500 library = 26.8 An hour; N is the equivalent of the battery reaction. This is the basic thermodynamic relationship between the battery electromotive force and the battery reaction, and it is also the basic thermodynamic equation for calculating the battery energy conversion efficiency. In fact, when the current passes through the electrode, the electrode potential must deviate from the thermodynamic equilibrium electrode potential. This phenomenon is called polarization. The greater the current density(the current passing through the unit electrode area), the more severe the polarization. Polarization is one of the important causes of battery energy loss. There are three reasons for polarization: 1 The polarization caused by the resistance of each part of the battery is called Ohmic polarization; The polarization caused by the block of charge transfer in the electrode-electrolyte interface layer is called activation polarization; The polarization caused by the slow transfer of mass in the electrode-electrolyte interface layer is called concentration polarization. The method of reducing polarization is to increase the electrode reaction area, reduce the current density, increase the reaction temperature, and improve the catalytic activity of the electrode surface.

Main Performance Parameters of Battery

The main properties of the battery include rated capacity, rated voltage, charge and discharge rate, impedance, lifetime, and self-discharge rate.

Rated capacity

Under the conditions specified in the design(such as temperature, discharge rate, termination voltage, etc.), the minimum capacity that the battery should be able to release, in amperes hours, is represented by symbol C. The capacity is greatly affected by the discharge rate, so the discharge rate is often indicated in Arabic numerals in the lower right corner of the letter C, such as C20 = 50, indicating that the capacity at the 20:00 rate is 50 An hour. The theoretical capacity of the battery can be accurately calculated based on the amount of electrode active material in the battery reaction formula and the electrochemical equivalent of the active substance calculated according to Faraday's law. Due to the possible side reactions in the battery and the special needs at the time of design, the actual capacity of the battery is often lower than the theoretical capacity.

Rated voltage

The typical operating voltage of the battery at room temperature is also called the nominal voltage. It is a reference for selecting different types of batteries. The actual operating voltage of the battery varies with different operating conditions. The open circuit voltage of the battery is equal to the difference of the equilibrium electrode potential of the positive and negative electrodes. It is only related to the type of electrode active substance, but not to the number of active substances. The battery voltage is essentially a DC voltage, but under certain special conditions, the phase transition of the metal crystal or some phase film caused by the electrode reaction will cause a slight fluctuation of the voltage. This phenomenon is called noise. The amplitude of the fluctuation is very small but the frequency range is very wide, so it can be distinguished from the self-excited noise in the circuit.

Charge and discharge rate

Sometimes the rate and the rate are two representations. The hourly rate is the charge and discharge rate expressed as the charge and discharge time, which is numerically equal to the number of hours obtained by dividing the battery's rated capacity(Ann hours) by the specified charge and discharge current(An). The factor is another representation of the charge and discharge rate, and its value is the reciprocal of the time rate. The discharge rate of the primary battery is expressed as the time from the discharge of a fixed resistance to the termination voltage. The discharge rate has a great influence on battery performance.

impedance

The battery has a large electrode-electrolyte interface area, so the battery can be equivalent to a series loop between a large capacitor and a small resistor and an inductor. However, the actual situation is much more complicated. In particular, the impedance of the battery changes with time and DC level. The measured impedance is only valid for the specific measurement state.

life

Storage life refers to the maximum period of time allowed to be stored from the time the battery is made to the beginning of use, in years. The total period of time, including storage and use, is the period of validity of the battery. The storage battery life is divided into dry storage life and wet storage life. The cycle life is the maximum number of cycles that the battery can achieve under the specified conditions. The system of charge and discharge cycle test, including charge and discharge rate, discharge depth and ambient temperature range, must be stipulated at the same time when the cycle life is specified.

Self-discharge rate

The rate at which the battery loses its capacity during storage. Expressed as a percentage of pre-storage capacity of self-discharge losses per unit storage time.

Chemical batteries

Chemical batteries refer to a type of device that converts the chemical energy of positive and negative active substances into electrical energy through electrochemical reactions. After a long period of research and development, chemical batteries have ushered in a wide variety of applications. As large as a huge device that a builder can accommodate, as small as a variety in millimeters. To serve our good life all the time. The development of modern electronic technology has put forward high requirements for chemical batteries. Every breakthrough in chemical battery technology has brought about a revolutionary development of electronic equipment. People in modern society are increasingly dependent on chemical batteries in their daily lives. Many electrochemical scientists around the world are now focusing their interest on chemical batteries that are powered by electric cars.

Dry and liquid batteries

The distinction between dry batteries and liquid batteries is limited to the period of early battery development. The earliest batteries consisted of glass containers filled with electrolytes and two electrodes. Later, a battery based on a paste electrolyte was introduced, also known as a dry battery.

There are still "liquid" batteries. It is generally a very large variety. For example, large fixed lead-acid batteries used as uninterruptible power supplies or lead-acid batteries used in conjunction with solar cells. For mobile devices, some use fully sealed, maintenance-free lead-acid batteries, which have been successfully used for many years. The electrolytic sulfuric acid is fixed by Silicon gel or absorbed by fiberglass partitions.

One-time and rechargeable batteries

One-time batteries are commonly known as "disposable" batteries because they can not be recharged and can only be discarded. Common disposable batteries include alkaline manganese batteries, zinc manganese batteries, lithium batteries, zinc batteries, zinc empty batteries, zinc Mercury batteries, Mercury batteries, hydrogen and oxygen batteries, and magnesium manganese batteries.

According to the materials and processes of the rechargeable batteries, common lead-acid batteries, nickel-cadmium batteries, nickel-iron batteries, nickel-metal hydride batteries, and lithium-ion batteries. Its advantage is that it has a long cycle life. They can be fully charged and discharged more than 200 times. Some rechargeable batteries have a higher load than most disposable batteries. In the use of ordinary nickel-cadmium and nickel-metal hydride batteries, the unique memory effect causes inconvenience in use and often causes early failure.

Theory of battery charging time

The theoretical charging time of the battery: The battery's power is divided by the output current of the charger.

For example: Take a battery with a charge of 800 MAH as an example. The output current of the charger is 500 MA. Then the charging time is equal to 800 MAH/500 MA = 1.6 hours. When the charger display is completed, it is best to give the battery about half an hour. Recharge time.

fuel cell

Fuel cells are devices that convert the chemical energy of a fuel directly into electrical energy through an electrochemical reaction. Fuel cells use hydrogen to perform an oxidation reaction at the anode, oxidize hydrogen to hydrogen ions, and oxygen performs a reduction reaction at the cathode. Combined with hydrogen ions from the anode to produce water. Current can be generated during the Redox reaction. Fuel cell technology includes the emergence of alkaline fuel cells(AFC), phosphate fuel cells(PAFC), proton exchange membrane fuel cells(PEMFC), molten carbonate fuel cells(MCFC), and solid oxide fuel cells(SOFC). And direct methanol fuel cell(DMFC), etc., and the use of methanol oxidation reaction as a positive reaction to fuel cell technology is also optimistic and positive development by the industry.

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